Logarithmic light intensifier for use with photoreceptor-based implanted retinal prosthetics and those prosthetics

ABSTRACT

This invention is for directly modulating a beam of photons onto the retinas of patients who have extreme vision impairment or blindness. Its purpose is to supply enough imaging energy to retinal prosthetics implanted in the eye which operate essentially by having light (external to the eye) activating photoreceptors, or photo-electrical material. The invention provides sufficient light amplification and does it logarithmically. While it has sufficient output light power, the output light level still remains at a safe level. Most preferred embodiments of this invention provide balanced biphasic stimulation with no net charge injection into the eye. Both optical and electronic magnification for the image, as for example, using an optical zoom lens, is incorporated. Otherwise, it would not be feasible to zoom in on items of particular interest or necessity. Without proper adjustment, improper threshold amplitudes would obtain, as well as uncomfortable maximum thresholds. Therefore, to adjust for these, a way of proper adjustment for the threshold amplitudes and maximum comfortable thresholds is provided. Furthermore, to the extent that individual stimulation sites in the retina give different color perceptions, upon stimulation, then colors of the viewed scene is correlated with specific stimulation sites to provide a certain amount of color vision.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application No.09/515,383, Filed Feb. 29, 2000, now U.S. Pat. No. 6,507,758.

This application claims the benefit of U.S. Provisional Application No.60/125,875, filed Mar. 24, 1999.

FIELD OF THE INVENTION

This invention, relates generally to retinal prosthetics and moreparticularly to a method and apparatus for enhancing retinal prostheticperformance.

This invention relates to directly modulating a beam of photons ofsufficient energy onto retinal prosthetic implants of patients who haveextreme vision impairment or blindness.

BACKGROUND OF THE INVENTION

A healthy eye is has photosensitive retinal cells (e.g. rods and cones)which react to specific wavelengths of light to trigger nerve impulses.Complex interconnections among the retinal nerves assemble theseimpulses which are carried through the optic nerve to the visual centersof the brain, where they are interpreted. Certain forms of visualimpairment are primarily attributable to a malfunction of thephotosensitive retinal cells. In such cases, sight may be enhanced by aretinal prosthesis implanted in a patient's eye. Michelson (U.S. Pat.No. 4,628,933) and Chow (U.S. Pat. Nos. 5,016,633; 5,397,350; 5,556,423)teach a retinal implant, or implants, of essentially photoreceptorsfacing out of the eye toward the pupil, each with an electrode which canstimulate a bipolar, or similar, cell with an electrical impulse. Thisbipolar cell is acted upon by the electrical stimulus, to sendappropriate nerve impulses essentially through the optic nerve, to thebrain.

This invention is postulated as a necessary complement to this type ofprosthesis, because the photoreceptors do not appear to be sensitiveenough to the ordinary levels of light entering the eye in that notenough current is produced to sufficiently stimulate the retinal cells.Consequently, a light amplifier, or “helper” device would be needed.That device is the invention herein described, which also includesspecial characteristic implants.

Furness, et al. teach a “virtual retinal display”, U.S. Pat. No.5,659,327, where “The virtual retinal display . . . utilizes photongeneration and manipulation to create a panoramic, high resolution,color virtual image that is projected directly onto the retina of theeye . . . there being no real or aerial image that is viewed via amirror or optics.” Richard, et al. teach, U.S. Pat. No. 5,369,415, “ . .. a direct retinal scan display including the steps of providing adirected beam of light, modulating the beam of light to impress videoinformation onto the beam of light, deflecting the beam in twoorthogonal directions, providing a planar imager including an input forreceiving a beam of light into the eye of an operator which involves aredirection diffractive optical element for creating a virtual imagefrom the beam of light on the retina of the eye, and directing the beamof light scanned in two orthogonal directions and modulated into theinput of the planar imager and the output of the planar imager into theeye of an operator.”

Sighted individuals can use these devices above for their intended uses.However, they appear unsuitable for use by blind individuals withimplanted retinal prosthetics of the photoreceptor-electrode kind. Itwould seem that they do not provide enough light power. Moreover, lightamplitude cannot be arbitrarily increased because according to Slinlyand Wolbarscht, Safety with Lasers and Other Optical Sources, theretinal threshold damage is 0.4 Joules per square centimeter.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus forproviding enhanced retinal prosthetic performance. More particularly,the invention is directed to a light amplifier and electrical circuitryfor driving an implanted retinal prosthesis to maximize electricalstimulation of the retinal nerves or cells, while avoiding damagethereto. The invention is also directed to improved implanted retinalprostheses, which maximize the advantages of the light amplifier.

In accordance with one aspect of the invention, light reflected from aviewed image (i.e., input image) is passed through a light amplifier toproduce an output image which is applied to the photoreceptor array of aretinal prosthesis. The gain (or “transfer function”) of the lightamplifier enables the photoreceptor array to drive output electrodes forproducing retinal nerve impulses of sufficient magnitude to enhanceperceived sight.

In accordance with another aspect of the invention, the light amplifierpreferably compresses the range of light intensity, e.g.,logarithmically, to enable maximum light amplification withoutoverdriving the prosthetic photoreceptors.

In accordance with another aspect of the invention, the electricalstimulation of the retinal nerves is preferably pulsed, i.e.,periodically interrupted to avoid any damage attributable to peakmagnitude electrical signals. Periodic interruption can be implementedmechanically by a shutter periodically interrupting the light incidenton the photoreceptor array and/or electrically via an appropriate waveshaping circuit.

In accordance with another aspect of the invention, the implantedprosthetic's electrodes generate a sequence of positive and negativepulses to avoid producing a net charge in the eye. Successive pulses arepreferably spaced in time by an interval Δt.

Four preferred embodiments are described. In accordance with the firstembodiment of the invention a single wavelength is relied upon toactivate a combined photodetector-electronics-electrode implanted unitwhich then produces a negative pulse, followed by a time delay, followedby a positive pulse. A photoreceptor implanted in the eye acts toproduce an electrical stimulation with an equal amount of positive andnegative charge. A single light wavelength is received by thephotoreceptor. That single wavelength contains extractable energy. Italso contains information, which may be encoded by amplitude modulation,frequency modulation, phase shift methods or pulse width modulation, forexample. The photoreceptor activates an electrode with associatedelectronics. The electronics produces a negative pulse followed by atime delay followed by a positive pulse. A net charge of zero isintroduced into the eye by the electrode-originating electrical pulses.The preferred delay time is in the range 0.1 millisecond to 10milliseconds, with the delay time of 2 milliseconds is most preferred.When the retinal cell is not being electrically stimulated, it returnsto a rest and recovery state. It is then in a state, electrically, thatit was in prior to stimulation by the first electrical stimulation.

In accordance with the second embodiment, a first wavelength is used tostimulate a first set of “electronic” photoreceptors. Thesephotoreceptors are connected so that the stimulation of the attached, orassociated, electrodes results in a negative pulse. This negative pulseprovides retinal cell stimulation. Then the shutter cuts in and stopslight transmission to the eye. The retinal cell is in a rest andrecovery state so that it returns, electrically, to the state it was inprior to stimulation by the first particular wavelength of light. Asecond particular wavelength of light then stimulates a second set ofphotoreceptors which are sensitive to that wavelength of light; whilethe first set of photoreceptors are not affected. This second set ofphotoreceptors is connected so that the stimulation of the attached, orassociated, electrodes results in a positive pulse. The net chargeintroduced into the retinal cells must balance. So the positive chargeintroduced by the positive pulse must equal the negative chargeintroduced by the negative pulse. Again, the shutter cuts in and stopslight transmission. Again, the retinal cells rest and recover and theprocess repeats. An aspect of the second embodiment is using anelectro-optic, electronic or mechanical shutter to provide a period ofno electrical stimulation to the retinal cells targeted for electricalstimulation.

In accordance with a third embodiment, which is a cross, so to speak,between the first and second embodiments two different wavelengths andtwo different types of diodes, each responsive to a correspondingwavelength are used. In this embodiment, one wavelength is used to pumpin a high constant level of light to supply power to the electronicscomponent. The other wavelength is used to send in information viaamplitude, frequency, phase, pulse-width modulation, or combinationsthereof. The stimulation pulse from the electronics to the electrode tothe retinal cell is generated in a fashion similar to the pulsesgenerated in the first embodiment, with a single wavelength.

A fourth embodiment is that of the logarithmic light amplifier itself,without any special implantable photoreceptors. This last embodiment mayrequire a low duty cycle when used with photoreceptors connected to adiode without any electronics. It may be able to rely sufficiently uponthe intrinsic capacitance of an oxidizable electrode, which acquirescapacitance with the buildup of an insulating oxidized layer toward theionizable fluid present in the eye as vitreous fluid, or fluid directlyassociated with the eye.

An image receiver with a first converter for the image, converts theimage into electrical signals. The signals are amplified, basicallylogarithmically, so as to provide brightness compression for thepatient.

An aspect of the embodiments of the invention is that an amplifiedelectrical signal is converted by a second converter into a photon-baseddisplay; the photons of this display enter an eye through the pupil ofthe eye. Moreover, while the embodiments of the logarithmic amplifierinvention have sufficient output light power, advantageously, the outputlight level still remains at a safe level. This aspect of the inventioncorresponds to aspects of the action of the iris, as well as thebiochemistry of retinal cells, in the human eye in making possible sightover many orders of magnitude of ambient brightness.

An aspect of the embodiments of the invention is incorporation of bothoptical and electronic magnification of the image, as for example, theincorporation of an optical zoom lens, as well as electronicmagnification. Consequently, it is feasible to focus in on items ofparticular interest or necessity.

With proper adjustment, proper threshold amplitudes of apparentbrightness would obtain, as well as comfortable maximum thresholds ofapparent brightness. Therefore, to adjust for these, an adjustmentaspect is incorporated in each embodiment, such that proper adjustmentfor the threshold amplitudes and maximum comfortable thresholds aremade.

Another aspect of the invention, which may be incorporated in allembodiments, is oriented toward making color vision available, at leastto a degree. To the extent that individual stimulation sites (e.g.,retinal cells generally, bipolar cells specifically) give differentcolor perceptions upon stimulation, the color of selected pixels of theviewed scene is correlated with a specificphotoreceptor-electronics-electrode units located so as to electricallystimulate a specific type of bipolar cell to provide the perception ofcolor vision.

In order to help implement both comfortable adjustment of threshold andmaximum brightness, and color vision, the logarithmic light amplifieralso incorporates within itself, a data processing unit which,semi-autonomously, cycles through the various photodetector-electrodeand combinations thereof, interrogates the patient as to what thepatient sees, the patient then supplies the answers, setting up properapparent brightness, proper apparent color and proper perception. Thissetup mode is done by the use of a keyboard, display, and auxiliaryprocessor, which are plugged into the data processing unit of thelogarithmic light amplifier during the setup procedure.

A scanning laser feedback is provided in different embodiments of theinvention to keep the scanner laser scanning the correct locations. Animaging of the reflected scanning laser reflected back from the retinalimplant is used to provide real-time feedback information, utilizing asecond imager viewing into the eye and a data processor unit tied intothe scanning laser scan control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the invention will bemore apparent from the following detailed description wherein:

FIG. 1 shows the logarithmic light amplifier with shutter, showing theincoming scene or view photons on the right and the eye on the left;

FIG. 2 a shows a laser being modulated by a video signal and scanningthe full extent of the implanted retinal prosthesis;

FIG. 2 b shows a photoreceptor, associated electronics, and anassociated electrode;

FIG. 2 c shows the apparatus of FIG. 2 b but in a more rounded, smootherpackaged form, likely more amenable for implantation into the eye;

FIG. 3 depicts tuned photodetectors on an implanted retinal prosthesis;

FIG. 4 shows a sample waveform possible with the apparatus shown in FIG.3;

FIG. 5 shows two different wavelengths, one to send in power, the otherto send in information, to a single unit with two differently sensitivephotoreceptors, one electronics package and one electrode;

FIG. 6 summarizes three embodiments as shown previously;

FIG. 7 shows the external logarithmic amplifier (as “glasses”), aportable computer with mouse and joystick as setup aids;

FIG. 8 shows an implant unit (old in the art) with a photoreceptor andan electrode;

FIG. 9 a shows a light-electronic feedback loop for knowing location onimplant being scanned;

FIG. 9 b shows one of different possible fiduciary markings includinghere points and lines for aiding knowing location on implant beingscanned.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is merely made for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

This invention provides amplified light for artificial photoreceptorsimplanted in the eye of a patient who has lost the use of his/her normalphotoreceptor retinal cells. The purpose of this amplified light is toeffectively stimulate the artificial photoreceptors. The artificialphotoreceptors, in turn, provide electrical stimulation throughassociated electrodes, usually via some electronics, to retinal cells,which are normally stimulated by living retinal photoreceptors such ascones and rods. The retinal cells, which get electrically stimulated byway of the artificial photoreceptors, are typically bipolar cells. Thisstimulation to these non-photoreceptor retinal cells allows the patientto have at least some perception of what a normal eye would see. Inorder not to damage the retinal cells, light is fed to thephotoreceptor-electrode stimulators in the following ways.

Four preferred embodiments are described. In the first embodiment asingle wavelength is relied upon to activate a combinedphotodetector-electronics-electrode implanted unit which then produces anegative pulse, followed by a time delay, followed by a negative pulse.In the first embodiment, a photoreceptor implanted in the eye acts toproduce an electrical stimulation with an equal amount of positive andnegative charge. A single light wavelength is received by thephotoreceptor. The photoreceptor activates an electrode with associatedelectronics. The electronics produces a negative pulse followed by atime delay followed by a positive pulse. A net charge of zero isintroduced into the eye by the electrode-originating electrical pulses.The preferred delay time is in the range 0.1 millisecond to 10milliseconds, with the delay time of 2 milliseconds is most preferred.When he retinal cell is not being electrically stimulated, it returns toa rest and recovery state. It is then in a state, electrically, it wasin prior to stimulation by the first electrical stimulation.

Starting with the logarithmic amplifier, an image receiver with a firstconverter for the image, converts the image into electrical signals. Thesignals are amplified, basically logarithmically, so as to providebrightness compression for the patient. The amplified electrical signalis converted by a second converter into a photon-based display; whereinsaid photons of said display enter an eye through a pupil of said eye.

Photons (102) from a viewed scene (not shown) enter the logarithmicamplifier (1000) by way of the lens (101). The light amplifier (1000)has an image receiver (1), a first converter (103) of the image intoelectrical signals, an amplifier (2) of said electrical signals wherebythe overall amplification of said electrical signal according to adefinite functional relationship between input signal to the amplifierand an output signal from the amplifier, a second converter (107) ofsaid amplified electrical signal into a photon-based display (7); suchthat the of display photons (108) enter an eye (5) through the pupil(105) of the eye (5). In the case where the imager (1) is a type ofvideo camera, the image receiver and conversion to electrical signalsmay occur in a package (old in the art).

A display (7) that is a source of photons such as a laser (coherentlight source) (7), or a non-coherent source such as colored LEDs (7), ora plasma display (7), is used to send photons directly to an implantnear the retina. These displays (7) are made very bright, but not suchas to impact negatively on the eye. In our cases, the patient hassufficient retinal degeneration so as to be unable to see without theaid of a retinal prosthetic. In the case where the display (photonsource) is a laser (7), that laser is 15 scanned over the implantedphotodetector-electronics-electrode array (FIG. 2, (8) in accordancewith the scene being displayed to the eye. A scanning laser is a laserwith scanning means (old in the art).

Referencing FIG. 2 a, the video signal (6) is applied to a scanninglaser (7), a scanning laser being a laser with scanning means (old inthe art). The scanning laser (7) is scanned over the retinal prosthesisin a square or rectangular pattern or in a raster pattern with an exactfit to the prosthesis (8). The video signal (6) supplies amplitude fromthe data processor (FIG. 1, (2)), and if desired (see FIG. 1), colorinformation, of the scene being viewed, from the individual coloramplifiers (3) to the laser (7), which information is used to modulatethe laser.

In a preferred mode, the light amplifier (1000) is a logarithmicamplifier. In another preferred mode, the amplifier amplifies accordingto a different function than the logarithmic function or a modifiedlogarithmic function, for example, an algebraic function such as apolynomial function multiplied by the logarithmic function.

The imager or camera lens is shown schematically as (101). The signal islogarithmically amplified as a whole at the electronic processor (2), orthe individual RGB (red, green, blue) or RGBY (red, green, blue, yellow)color components are individually logarithmically amplified (3). Anothercolor component mix of white light may be used. The individualamplification (3) of separate color components allows for the relativesuper-amplification of one color to which the photoreceptors areparticularly sensitive. If only a “black-and-white” contrast image isdisplayed, the “white” part of that image is logarithmically translatedto the color, i.e., wavelength, to which the photoreceptors are mostsensitive. This feature includes shifting the wavelength toward or tothe near infrared or toward or to the near ultraviolet, according towhat is needed to optimize the response of the implanted photosensitiveelements. Consequently, a mapping of the incoming image data to anappropriate output is possible. This mapping could be complex, forexample, producing biphasic waveforms as shown in FIG. 4 by appropriatetiming of two lasers operating at different wavelengths andphotosensitive elements uniquely sensitive to these wavelengths.

In a preferred mode, individual RGB (red, green, blue) or RGBY (red,green, blue, yellow) color components are amplified separately (3), oramplified together (2) and separated out (3) after the amplification.These color components may be used to stimulate particularphotosensitive elements of the retinal implant(s). For example, a cell(“blue-sensation”) producing a sensation of blue color is stimulatedwhen the scene being transmitted to the eye has blue, which in theprojected (into the eye) scene would have blue in the vicinity of thatblue-sensation cell.

The logarithmic amplification is necessary to compress the range oforiginal brightness. The normal eye does this automatically of closingdown the pupil size, squinting and employing other electrochemicalcellular mechanisms. This light amplifier accomplishes this necessarytask by electronic logarithmic light amplification. The light amplifieralso includes an adjustable transformer or magnification of image size.A shutter or electronically turning the scanning laser on and off arenot a necessary part of this embodiment.

In the second preferred embodiment of the light amplifier two or morewavelengths are used to communicate light energy to the eye to allowbalanced biphasic stimulation with no net charge injection into the eye.A first wavelength is used to stimulate a first set of photoreceptors.These photoreceptors are connected so that the stimulation of theattached, or associated, electrodes results in a negative pulse. Thisnegative pulse provides retinal cell stimulation. Then the shutter cutsin and stops light transmission to the eye. The time of this lightinterruption is preferred in the range 0.1 millisecond to 10milliseconds, with the time of 2 milliseconds most preferred. Theretinal cell is in a rest and recovery state so that it returns,electrically, to the state it was in prior to stimulation by the firstparticular wavelength of light. A second wavelength of light thenstimulates a second set of photoreceptors which are sensitive to thatwavelength of light; while the first set of photoreceptors are notaffected. This second set of photoreceptors is connected so that thestimulation of the attached, or associated, electrodes results in apositive pulse. The net charge introduced into the retinal cells mustbalance, or equal, the net charge introduced by the negative pulse.Again, the shutter cuts in and stops light transmission. Again, theretinal cells rest and recover and the process repeats.

In the second preferred embodiment, FIG. 3A, two scanning lasers, (9)and (10), are supplied with video signals, with each laser operating ata different wavelength. Advantageously, two or more photoreceptors (13),(14) are on the implant. The two types of photoreceptors (13), (14), aretuned to different frequencies of light, each of the frequencies beingthat of one of the emitting frequencies of the external lasers (9),(10). FIG. 3B shows two incoming frequencies of light, (301) and (302).The light sources for the dual light frequencies (301), (302) is a unit(304) which is downstream in the information flow from the imager (FIG.1, (101), (1), (103)) and amplifiers (FIG. 1, (2), (3)). The finaloutput from the amplification stages is connected electrically orelectromagnetically to the dual light frequency sources (304), inparticular, dual scanning lasers operating with different wavelengths oflight output. Pairs (303) of different frequency (i.e., wavelength)photoreceptors are placed on the eye-implant, each pair associated withan electrode (not shown).

Together, the two types of photoreceptors (e.g., photodiodes) give riseto a biphasic current (FIG. 4) at each electrode (not shown). Initiallythe rest state appears (40). Next, one of the photoreceptors (13) hasbeen activated by its corresponding laser (9). The current amplitude isnegative. (41). After a time (42), laser (9) and photoreceptor (13) shutdown and the amplitude returns to zero. Next, the other laser (10)actives its corresponding (in light wavelength) photoreceptor (14) andthe amplitude is positive by an amount (43) and for a duration (44).Nominally, in absolute value, (41)=(43), and (42)=(44). However, in thecase this is not exact, then the parameters (44) and (43) can be alteredsuch that (41)*(42)=(43)*(44), where * indicates multiplication. Thiscan be accomplished by measuring (41) and (42) and then altering (43) or(44) or both to maintain charge balance.

A shutter (4) is part of the second embodiment. The shutter (FIG. 1,(4)) is of a mechanical design (old in the art), or an electronicshutter (4) (old in the art) or an electro-optical shutter (4) (old inthe art). The shutter (4) cuts off light from the logarithmic lightamplifier (1000) to the pupil (105) of the eye (5). This decreases thetotal time that light strikes the photoreceptors (FIG. 3 a, (13), (14)),(FIG. 3 b, 303) Consequently, the time during which the bipolar, orsimilar cells, are stimulated is decreased. Because the eye is notfunctioning as originally intended, the bipolar, or similar, cells arethought to need this “down-time” to continue to function properly.

An aspect of this invention is the use of two or more wavelengths toallow balanced biphasic stimulation with no net charge injection intothe eye. As long as a biphasic type of electrical stimulation, whereequal amounts of positive charge and negative charge in the form ofionic carriers or electrons or other charge carriers, enter the vitreousfluid of the eye, the electrical effect on the eye is not harmful. Ifdirect current is supplied to the eye, internally, a charge imbalanceresults. This excess of charge has been found to be harmful to cells.Consequently, direct current can harm the bipolar and other cells.Advantageously, the biphasic electrical stimulation tends to avoid thisharm to the cells because no excess charge accumulates.

A third embodiment that is a cross, so to speak, between the first andsecond embodiments uses two different wavelengths and two differenttypes of diodes, each responsive to a corresponding wavelength. In thisembodiment, one wavelength is used to pump in a high constant level oflight to supply power to the electronics component. The other wavelengthis used to send in information via amplitude, frequency, phase,pulse-width modulation, or combinations thereof. The stimulation pulsefrom the electronics to the electrode to the retinal cell is generatedin a fashion similar to the pulses generated in the first embodiment,with a single wavelength.

The third embodiment uses two different wavelengths and two differenttypes of diodes, each responsive to a corresponding wavelength. (SeeFIG. 3 b, (301), (302)). In this embodiment, one wavelength (FIG. 5,(501)) is used to pump in a high constant level of light to supply powerto the electronics component (502). The other wavelength (503) is usedto send in information via amplitude, frequency, phase, pulse-widthmodulation, or combinations thereof to the electronics component (502).The stimulation pulse from the electronics (502) to the electrode (504)to the retinal cell is generated in a fashion similar to the pulsesgenerated in the first embodiment, with a single wavelength.

See FIG. 6. FIG. 6 summarizes in block form the preceding threeembodiments. In the first embodiment there is one wavelength (601) inputto a single diode (602) with electronics (603) and electrode (604).Either digitally or by analogue means, old in the art, a d. c. signaloccurring after the absorption of photons by the photoreceptor isconverted by the electronics to a signal (600) of the type shown in FIG.4, at the electrode. In the second embodiment, for two differentwavelengths (610), (611), both carrying power and information, impingingon two different photoreceptors (612), (613), the electronics (6033),digital or analogue, again produce the waveform (600) of FIG. 4 at theelectrode (604). In the third embodiment, for two differentphotoreceptors (620), (621), the first receiving a steady state powerwavelength (622), the second receiving a signal wavelength (623), theelectronics (6034), digital or analogue, produces the signal (600) ofFIG. 4 at the electrode (604). The electronic circuitry of (603), (6033)and (6034) may be different.

A fourth embodiment is that of the logarithmic light amplifier (1000)itself, without any special implantable photoreceptors. This lastembodiment may require a low duty cycle when used with photoreceptors(FIG. 8, (81)) connected to an electrode (82) without any electronics.It relies upon the intrinsic capacitance of an oxidizable electrode,which acquires capacitance with the buildup of an insulating oxidizedlayer toward the ionizable fluid present in the eye as vitreous fluid,or fluid directly associated with the eye.

In a first set of embodiments, the addition of a shutter (FIG. 1, (4))with an off time of from 0.5 ms to 10 ms, most preferably 2 ms providesa mechanism to provide that off time (FIG. 4, (47), (48)). However, in asecond set of embodiments, the time each laser is on can be controlledby electronic means (old in the art) within the laser to provide equalpositive pulses and negative pulses, i.e., equal with respect to totalsigned charge introduced into a retinal cell. The first and second setsof embodiments may be completely or partially coincident.

Another aspect of all of the embodiments is incorporation of bothoptical and electronic magnification of the image, as for example, theincorporation of an optical zoom lens, as well:as electronicmagnification. Optical magnification of the image (see FIG. 1) isaccomplished by use of a zoom lens for the camera lens (101). Electronicmagnification is accomplished electronically in an electronic dataprocessing unit (2) or (3). Consequently, it is feasible to focus in onitems of particular interest or necessity.

With proper adjustment, proper threshold amplitudes of apparentbrightness obtain, as well as comfortable maximum thresholds of apparentbrightness. Therefore, to adjust for these, a sixth aspect isincorporated in all of the embodiments such that proper adjustment forthe threshold amplitudes and maximum comfortable thresholds can be made.

To makes color vision available, to a degree; another aspect isincorporated. To the extent that individual stimulation sites (e.g.,bipolar cells) give different color perceptions upon stimulation, thecolor of selected pixels of the viewed scene is correlated with aspecific pair of photoreceptors located so as to electrically stimulatea specific type of bipolar cell to provide the perception of colorvision

In order to help implement these last two aspects of the preferredembodiments of this invention, apparent brightness control and thepresentment of apparent color, the logarithmic amplifier alsoincorporates within itself, a data processing unit which cycleselectrical pulses of varying amplitude and/or frequency and/or phaseand/or pulse width through the various photodetector-electrodes andspatial combinations thereof, and, interrogates the patient, who thensupplies the answers, setting up proper apparent brightness and apparentcolor. A different aspect of the embodiments utilizes a plug inaccessory data processor (FIG. 7, (71)) with display (72) and data inputdevice or devices such as a keyboard (73), mouse (74), or joystick (75).FIG. 7 show the plug in unit (71) which plugs (76) into the logarithmiclight amplifier (1000) to provide additional data processing ability aswell as expanded data input and data display capability.

In order for the scanning laser to correctly scan the retinal implantprosthetic photoreceptors, it is helpful if some feedback is provided toit. One aspect of the different embodiments is the presence of afeedback loop using some of the reflected light from the scanning laseritself. One aspect of the feedback loop is to use regions of differentreflectivity on the surface of the retinal implant which allow thelocation, or relative location, of the scanning laser light beam to bedetermined.

A scanning laser feedback is provided in the different embodiments ofthe invention. An imaging (FIG. 9 a) of the retinal implant from thereflected (92) incoming scanning laser beam (91), see FIG. 9 a, (7),(FIG. 1 and FIG. 2 a, (7)), (FIG. 3 a, (9,), (10)) reflected back fromthe retinal implant (FIG. 9, (8)) can be used to provide real-timefeedback information, utilizing a second imager (93) viewing into theeye (5) and a data processor unit (94) tied into the scanning laser'sscan control unit (95).

Another aspect of the embodiments (FIG. 9 b) utilizes multiple fiduciaryreflective or light absorptive points (96) and/or lines (97) on theretinal implant (8) such that the frequency and signal pattern, moregenerally, (98), (99), (100) of the high reflectivity from thesereflective, or absorptive lines/point for a given rate of scanning bythe scanning laser (7) can be used to correct the scanning directionfrom the different frequency patterns, some indicating correct scanning,others indicating an incorrect scanning.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

1. A retinal prosthesis comprising: a light receiver for collection of areceived visual image; an amplifier coupled to said light receiver,amplifying said received visual image in accordance with a non-lineartransfer function; an electrode array coupled to said amplifier suitablefor stimulating a retina; and control means for interrupting said signalbetween a positive and a negative pulse.
 2. The retinal prosthesisaccording to claim 1, wherein said non-linear transfer function is alogarithmic function.
 3. The retinal prosthesis according to claim 2,wherein said non-linear transfer function is a logarithmic compressionfunction.
 4. The retinal prosthesis according to claim 1, furthercomprising control means for temporarily interrupting said receivedvisual image.
 5. The retinal prosthesis according to claim 1, furthercomprising a size transformer of said received visual image.
 6. Theretinal prosthesis according to claim 5, wherein said size transformerof said received visual image is a magnifier for magnifying saidreceived visual image.
 7. The retinal prosthesis according to claim 6,wherein said magnifier is an optical zoom lens.
 8. The retinalprosthesis according to claim 1, wherein said amplifier produceselectrical signals imposing no net charge upon the retina.
 9. Theretinal prosthesis according to claim 8, wherein said electrical signalsare alternating electrical signals.
 10. The retinal prosthesis accordingto claim 9, wherein said alternating electrical signals are biphasicpulses.
 11. The retinal prosthesis according to claim 10, wherein saidbiphasic pulses comprises a negative pulse followed by a positive pulse.12. A method of operating a retinal prosthesis comprising: receiving areceived visual image; amplifying said received visual image inaccordance with a non-linear transfer function to produce an amplifiedvisual image; energizing an electrode array according to said amplifiedvisual image; and temporarily interrupting said received visual image.13. The method according to claim 12, wherein said non-linear transferfunction is a logarithmic function.
 14. The method according to claim12, wherein said non-linear transfer function is a logarithmiccompression function.
 15. The method according to claim 12, furthercomprising the step of temporarily interrupting said received visualimage.
 16. The method according to claim 12, further comprising the stepof transforming the size of said received visual image.
 17. The methodaccording to claim 16, wherein said step of transforming the size ofsaid received visual image comprises magnifying said received visualimage.
 18. The method according to claim 17, wherein said step ofmagnifying is accomplished by an optical zoom lens.